The Muscle Physiology Core is a well equipped in vitro physiology laboratory staffed with experienced personnel skilled in executing personnel skilled in executing the proposed contractile studies. This Core will be supervised by Jon Watchko, M.D., and be available to all principal investigators assisting them in achieving their research goals evaluating the effects of gene therapy on skeletal muscle function. In addition to meeting the overlapping needs of individual projects and thereby being the most efficient use of space, equipment and personnel talent, this Core will enhance collaboration between investigators. The Specific Aims of the Muscle Physiology ore are to i) obtain natural history data on muscle function of the tibialis anterior in normal and dystrophic (dystrophin-deficient mdx) mice, and normal and dystrophic cardiomyopathic) hamsters, and ii) determine the positive or negative effects of viral vector gene delivery on contractile function of the tibialis anterior muscle of dystrophin deficient mice and delta- sarcoglycan hamsters.